1. Field of the Invention
The field of the present invention is valve operating systems for internal combustion engines, comprising a valve operation mode changing mechanism capable of changing the amount of lift opening of an engine valve openably and closably carried in an engine body and/or the opening or closing timing to correspond to engine speed for improving the engine operation. The change is accomplished in many systems by a variation in hydraulic pressure supplied to the mechanism by means of a selector valve having a slidable valve element to control the condition for supplying the hydraulic pressure to the valve operation mode changing mechanism.
2. Description of the Prior Art
Such valve operating system has conventionally been known, for example, from Japanese Patent Application Laidopen No. 226216/84 (corresponding to U.S. Pat. No. 4,537,165).
In such a valve operating system, the hydraulic pressure supplied to the valve operation mode changing mechanism is changed to a higher or lower level by a selector valve to operate the valve operation mode changing mechanism, thereby changing the opening and closing mode for the engine valve, and it is desirable that such changing of the hydraulic pressure is conducted quickly to provide a rapid and smooth changing operation of the valve operation mode changing mechanism.